Air cooled semiconductor stack

ABSTRACT

A pair of end plates having windows sandwiches an alternate assembly of semiconductor elements and finned cooling members and is fastened by stud bolts to form a semiconductor stack. The windows of the end plates serve to pass a flow of cooling air in the direction of the longitudinal axis of the stack. Cooling fins on the cooling members extend along and substantially radially with respect to the longitudinal axis of the semiconductor stack.

[22] Filed:

United States Patent 1191 Oshima [54] AIR COOLED SEMICONDUCTOR STACK[75] Inventor: Seiichi Oshima, Itami, Japan [73] Assignee: MitsubishiDenki Kabushiki Kaisha,

' 7 Tokyo, Japan Aug. 3, 1971 211 Appl. No.1 168,559

[52] U.S Cl. 317/234 R, 317/234 A, 317/234 P, 317/234 W, 165/80 [51]Int. (:1. ..H0ll 3/00, 110115/00 [58] FieldofSearch ..317/234,235, 1,317/1.5,6, 11; 165/80 [56] References Cited v- I UNITED STATES PATENTS1345,57'3 2/ 1'9321 Ackerly....;.... ...i... ..317/234 2,486,768 11/1949Walker; ..317/234 12/1957 Jackson et a]. ..3l7/234 1451 Apr. 10, 19733,280,389 10/1966 Martin ..317/234 3,364,987 l/l968 Bylund et a1. .317/234 FOREIGN PATENTS OR APPLICATIONS 905,361 9/1962 Great Britain ..31 7/234 710,282 9/1941 Germany ..3 1 7/234 Primary ExaminerJohn W.I-luckert Assistant Examiner-Andrew .1. James Attorney-E. F. Wenderothet al.

[57] ABSTRACT A pair of end plates having windows sandwiches analternate assembly of semiconductor elements and finned cooling membersand is fastened by stud bolts to form a semiconductor stack. The windowsof the end plates serve to pass a flow of cooling air in the directionof the longitudinal axis of the stack; Cooling fins on the coolingmembers extend alongand substantially radially with respect to thelongitudinal axis of the semiconductor stack.

6 Claims, 5 Drawing Figures PATENTEDAPM mm 3.727, 114

SHEET 1 BF 2 FIG. 10 FIG. 1b

FIG. 2

SEIICHI USHIMA,

INVENTOR ATTORNEY r.

PMENTEDAPR 1 01975 SHEET 2 []F 2 FIG. 3

SEIICHI 6sHIMA,

INVENTOR A'T'I'OR NEY S AIR COOLED SEMICONDUCTOR STACK BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to a pressurecontact type semiconductor stack having an improved cooling structure.

2. Description of the Prior Art The conventional pressure contact typesemiconductor stack has comprised a plurality of pressure contact typeflat package type semiconductor elements and aplurality of coolingmembers having circumferencially extending cooling fins, thesemiconductor elements andthe cooling members being brought in apressure contact relationship by means of a pair of end plates and studbolts. To cool such a conventional semiconductor stack by air, the stackhas been so positioned in a wind tunnel that its longitudinal axisintersects at substantially right angles with a flow direction ofcooling air produced by a powerful pressure blower.

With the conventional system for cooling the semiconductor stack,however, because the semiconductor stack has had to be transverselyplaced in a wind tunnel, the diameter of the wind tunnel used hasinevitably been changed in accordance with the overall length of thestack. Also, since the smallest blower easily available in the market isof about 300 4: mm in diameter, the overall dimensions of the systemincluding a wind tunnel cannot be reduced to reasonable values even whenthe semiconductor stack itself is small in dimensions.

SUMMARY OF THE INVENTION Accordingly, an object of the invention is toprovide a pressure contact type semiconductor stack having an improvedcooling structure suitable for use in such a stack. I

Another object of the invention is to provide a pressure contact typesemiconductor stack having a compact and economical cooling structure.

Still another object of the invention is to provide a pressure contacttype semiconductor stack having improved end plates and improved coolingmembers especially suitable for use in cooling the semiconductor stack.

Further object of the invention is to provide a pressure contact typesemiconductor stack with a blower directly mounted to the stack.

Still further object of the invention is to provide a pressure contacttype semiconductor stack capable of being effectively cooled withoutemploying a wind tunnel.

In view of the above objects, the pressure contact type semiconductorstack of the present invention is arranged to be cooled by a flow ofcooling air flowing along the longitudinal axis of the stack. For thispurpose, the semiconductor stack comprises a plurality of semiconductorelements, a plurality of cooling members disposed alternately with thesemiconductor elements, and a pair of end plates and stud bolts forassembling the semiconductor stack. The cooling fins on the coolingmembers extend along and substantially radially with respect to thelongitudinal axis of the semiconductor stack, and the end platesdisposed on both ends of the stack have some windows for permitting aflow of cooling air to pass therethrough in the direction of thelongitudinal axis of the stack. One of the end plates may be so arrangedthat a blower is directly mounted thereon.

BRIEF DESCRIPTION OF THE DRAWING semiconductor stack shown in FIGS. 1aand 1b; and

FIG. 4 is a plan view similar to FIG. 1a but showing the semiconductorstack with a blower.

Throughout several Figures the same reference characters designateidentical or corresponding components.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawingsand in particular to FIGS. la and 1b, a pressure contact typesemiconductor stack constructed in accordance with the present'invention comprises two pressure contact type semiconductor elements IAand 1B of a known type such as flat package type thyristors or flatpackage type diodes, which, if desired, may increase or decrease innumber. It is to be noted that although the illustrated semiconductorstack has semiconductor elements arranged in an electrically seriesrelationship, the arrangement can be modified by inserting any suitableinsulating material into the proper position between the semiconductorelements.

The semiconductor elements 1A and 1B are directly sandwiched between thecooling members 2A and 2B and between the cooling members 2B and 2Crespectively. In other words, two semiconductor elements IA and 1B andthree cooling members 2A, 2B and 2C constitute an alternating assembly.The assembly thus arranged is sandwiched by a pair of end plates 3A and3B and fastened by four stud bolts 4 extending between the pair of endplates 3A and 33. Each of the stud bolts 4 extends through guide boresformed on the end plates 3A and 3B and guide bores formed on the coolingmembers 2A, 2B and 2C which will be described later in detail inconjunction with FIGS. 2 and 3.

In order to electrically insulate the semiconductor elements 1A and 1Band the cooling members 2A, 2B and 2C from any other components such asthe end plates 3A and 3B and the stud bolts 4, an insulating tube 5 ofany suitable insulating material is applied to the stud bolts 4 betweenboth the end plates 3A and SE to cover the peripheral surface thereof.Each of the stud bolts 4 has a screw threaded portion on its one end forengagement of a nut 6. Thus the stud bolts 4 produce a compression forcewhich establishes a pressure contact relationship on the respectivecontact faces between the semiconductor elements IA and 1B and thecooling members 2A, 2B and 2C.

The compression force produced by the stud bolts 4 and the nuts 6 shouldbe modulated into a predetermined value profitable for the semiconductorelements 1A and 1B. For this purpose, disc springs 7 and an electricallyinsulating washer 8 are disposed between the end plate 3A and thecooling member 2A. In order to ensure that the compression force isuniformly distributed to provide a uniform pressure contact relationshipto the contact faces between the semiconductor elements and the coolingmembers, an insulating washer 9 and a self-aligning seat 10 are disposedbetween the end plate 3B and the cooling member 2C.

FIG. 2 shows one of the cooling members for use in the semiconductorstack shown in FIGS. la and lb. The cooling member 2 made of anysuitable electrically conductive and heat conductive material comprisesa substantially circular support portion 21 for supporting thesemiconductor elements in pressure contact relationship, four legportions 22 extending from the support portion 21 at equal angularintervals, a plurality of cooling fins 23 symmetrically extending fromboth sides of each of the legs 22 in such a relationship that they arein parallel with the longitudinal axis of the semiconductor stack, i.e.,the axis along which the semiconductor elements are stacked, and thatthey intersect at angles of 45 with the axes of the legs 22. The coolingmember further comprises a guide bore 24 for guiding the stud bolts 4formed on the extremity of each of the legs 22, and two parallelterminal portions 25 extending in the same direction from two selectedend portions of the legs 22. The terminals 25, which are considered tobe elongated cooling fins 23, are connected to an external circuit (notshown).

FIG. 3 shows one of the end plates 3 for use in the semiconductor stackshown in FIGS. la and 1b. The end plate 3 comprises a support portion 31similar to the support portion 21 of the cooling member 2. The supportportion 31 has four leg portions 32 radially extending therefrom atequal angular intervals. The end plate 3 further comprises a rectangularframe portion 33 connected at its corners to the respective extremitiesof the legs 32. Thus the end plate 3 has four substantially triangularwindows 34, which are defined by the legs 32 and the frame 33, forpermitting the flow of cooling air to pass therethrough. On each of thelegs 32, there is provided a bore 35 for guiding the stud bolt 4previously described in conjunction with FIGS. la and lb at thatposition corresponding to the guide bore 24 of the cooling member 2.

In order to combine the semiconductor stack with another similarsemiconductor stack, the end plate 3 may have bores 36 on the frame 33through which the stacks to be combined can be put together by means ofbolts and nuts for example.

To cool the semiconductor stack thus constructed, a flow of cooling airproduced by any type of blower is supplied in the direction of thelongitudinal axis of the stack as shown by the arrows of FIG. la. Thenthe flow of cooling air passes through the windows 34 of the end plate3A to flow between the cooling fins 23 formed around the cooling members2A, 2B and 2C, thereby to cool the semiconductor elements which arebrought in the pressure contact relationships with the cooling members2.

It is known that, when a flow of air of a speed of from 1 to 2 m/sec isapplied to the semiconductor stack thus constructed, the thermalresistance of the cooling member is reduced to from three-fourth toone-half of that under the natural cooling condition, and that such aflow speed is sufficiently high for effectively cooling thesemiconductor stack. For applying a flow of air of such a relatively lowspeed, it is not required to install a wind tunnel around thesemiconductor stack. Therefore, the semiconductor stack of the presentinvention eliminates the necessity of employing a wind tunnel.

Although the flow of cooling air may be produced by any type ofconventional system, it is of great convenience in practical use todirectly mount a blower to the semiconductor stack.

FIG. 4 illustrates the pressure contact type semiconductor stack with acooling fan or a blower 11 directly attached to one of the end plates3A. The blower 11 which may be of any conventional type is mounted tothe frame 33 of the end plate 3A by means of screws 12 and the screwthreaded bores formed on each comers of the frame portion 33. When theblower 11 is energized by an electrical source (not illustrated), a flowof air designated by the arrows is produced and it passes through thewindows 34 of the end plate 3A to flow between the cooling fins 23formed on the cooling members 2A, 2B and 2C, thereby to cool thesemiconductor elements 1A and 1B. Thereafter, the air flow leaves thesemiconductor stack through the windows 34 of the end plate 3B.

Although the semiconductor stack illustrated in FIG. 4 has only oneblower on its one of the end plates 3A, if the overall length of thestack becomes long and effective cooling of the cooling member remotefrom the blower cannot be expected, an additional blower similar to thatillustrated may be mounted on the other end plate 38. For this purpose,the end plate 38 may also have screw threaded bores similar to those ofthe end plate 3A on its corners.

With the arrangement of the semiconductor stack as has heretofore beendescribed, the stack can be effectively cooled by a relatively small andless powerful blower without employing a wind tunnel. Therefore thewhole system of the semiconductor stack including a blower can be madecompact and simple in construction. Also, since the semiconductor stackis arranged to be cooled by an air flow flowing along its longitudinalaxis, even when the number of the semiconductor elements used increases,it is only the overall length of the stack that increases, and thediameter of the blower is not required to be increased. This provides anincrease in exchangeability of the components, leading to an economicalarrangement.

Furthermore, the semiconductor stack does not produce noise as with theconventional cooling system employing a wind tunnel. In addition,mounting and dismounting of the blower 1 1 can be easily perfonned.

What I claim is:

l. A pressure contact type semiconductor stack comprising a plurality ofsemiconductor elements, a plurality of cooling members each having aplurality of cooling fins and disposed in alternately stackedrelationship with said semiconductor elements, said cooling fins beingformed in parallel with and substantially radially with respect to theaxis along which the semiconductor elements and the cooling members arestacked, a pair of end plates sandwiching said semiconductor elementsand said cooling members therebetween in the direction in which thesemiconductor elements and the cooling members are stacked, and holdingmeans for holding said semiconductor elements and said cooling membersbetween said pair of end plates to establish pressure contactrelationship therebetween, each of said end plates having windows for aflow of cooling air, thereby to cool the semiconductor stack by a flowof cooling air flowing in the direction of the axis along which thesemiconductor elements and the cooling members are stacked.

2. A pressure contact type semiconductor stack as claimed in claim 1,wherein each of said end plates comprises support means for supportingsaid semiconductor elements and said cooling members, plurality of legportions radially extending from said support means, and a frame portionconnecting extremities of said 'leg portions, thereby to form saidwindows for the flow of cooling air.

3. A pressure contact type semiconductor stack as claimed in claim 2,wherein each of said leg portions has a guide bore for guiding saidholding means, which are stud bolts.

4. A pressure contact type semiconductor stack as claimed in claim 1,wherein each of said cooling members comprises support means forsupporting said semiconductor elements, a plurality of leg portionsradially extending from said support means, and a plurality of saidcooling fins extending from said leg portions in parallel with andsubstantially radially with respect to said axis along which thesemiconductor elements and the cooling members are stacked.

5. A pressure contact type semiconductor stack as claimed in claim 4,wherein each of said leg portions of the cooling members has a guidebore for guiding said holding means, which are stud bolts.

6. A pressure contact type semiconductor stack as claimed in claim ll,wherein at least one of said end plates has a blower directly mountedthereon, thereby to produce a flow of cooling air flowing in thedirection of the axis along which the semiconductor elements and thecooling members are stacked.

1. A pressure contact type semiconductor stack comprising a plurality ofsemiconductor elements, a plurality of cooling members each having aplurality of cooling fins and disposed in alternately stackedrelationship with said semiconductor elements, said cooling fins beingformed in parallel with and substantially radially with respect to theaxis along which the semiconductor elements and the cooling members arestacked, a pair of end plates sandwiching said semiconductor elementsand said cooling members therebetween in the direction in which thesemiconductor elements and the cooling members are stacked, and holdingmeans for holding said semiconductor elements and said cooling membersbetween said pair of end plates to establish pressure contactrelationship therebetween, each of said end plates having windows for aflow of cooling air, thereby to cool the semiconductor stack by a flowof cooling air flowing in the direction of the axis along which thesemiconductor elements and the cooling members are stacked.
 2. Apressure contact type semiconductor stack as claimed in claim 1, whereineach of said end plates comprises support means for supporting saidsemiconductor elements and said cooling members, plurality of legportions radially extending from said support means, and a frame portionconnecting extremities of said leg portions, thereby to form saidwindows for the flow of cooling air.
 3. A pressure contact typesemiconductor stack as claimed in claim 2, wherein each of said legportions has a guide bore for guiding said holding means, which are studbolts.
 4. A pressure contact type semiconductor stack as claimed inclaim 1, wherein each of said cooling members comprises support meansfor supporting said semiconductor elements, a plurality of leg portionsradially extending from said support means, and a plurality of saidcooling fins extending from said leg portions in parallel with andsubstantially radially with respect to said axis along which thesemiconductor elements and the cooling members are stacked.
 5. Apressure contact type semiconductor stack as claimed in claim 4, whereineach of said leg portions of the cooling members has a guide bore forguiding said holding means, which are stud bolts.
 6. A pressure contacttype semiconductor stack as claimed in claim 1, wherein at least one ofsaid end plates has a blower directly mounted thereon, thereby toproduce a flow of cooling air flowing in the direction of the axis alongwhich the semiconductor elements and the cooling members are stacked.